Gram-negative germs (e.g. cholera germs, salmonella germs, colon bacillus) have substances known as lipopolysaccharides (abbreviated as LPS hereafter) on the outer cell membrane, and it is considered that such substances induce endotoxin shock.
It is known that LPS have various bioactivities including fetal toxicity; this is why it is so named on endotoxin. For example, LPS have an enhancing activity of immunity which is a defensive system of a host (macrophage-activating action, B cell mitogenic activity, producing activity of non-specific antibody, enhancing activity of cellular immunity, etc.) and anti-tumor activity (interferon-inducing activity, TNF (tumor necrosis factor)-inducing activity etc.), besides a pyrogenetic activity and a hemorrhage activity. Especially, LPS is effective as a non-specific immunity agent to any antigens. LPS also has an action specifically inducing hemorrhage necrosis of tumor cells by its TNF-inducing activity, and therefore, can be useful as an anti-tumor agent.
Furthermore, its inducing activity of interleukin-1 or of interferon makes LPS useful as not only agent for enhancing immunity but also anti-tumor agent by stimulating natural killer activity.
It is known that the active center of LPS is a disaccharideamine, called lipid A, and may patent applications on derivatives of lipid A have been already filed.